This is a continuation of the issue that occurs in Illustrator CS6
This seems to only be an issue with the "export for screens" option. I'm guessing this is a bug that just hasn't been solved yet.
If anyone has any insights regarding solutions, feature requests, or bug fixes please add them in the comments.
If I create a New Illustrator document with Web intent and define an artboard size in pixels, exporting for screens gives me an exact artboard size: in other words, I can't replicate the problem in Illustrator CC (2018) and do NOT see an extra pixel in width or height.
I'm wondering if step 2 in your settings is the culprit – and possibly due to stroke weights and stroke positioning, there is a minuscule bit of 'rounding' occurring that when exported for screens results in a rounding up.
Are you able to provide some step-by-step screenshot examples of what you are doing?
Steps to Reproduce
File > Export > Export for Screens...
Export for Screens
(some images and text censored)
Windows 10 Explorer > [right click newly created PNG] > Properties
(some images and text censored)
I realize this issue was brought up last year, but I had the same problem and thought it helpful to share a potential solution. Making sure the artboard is aligned to the pixel grid as described at https://www.reddit.com/r/AdobeIllustrator/comments/3dqadd/1_pixel_off_when_exporting_artboards_to_pn... fixed the additional pixel problem in my situation. Essentially, while using the Artboard Tool make sure the X and Y position values are whole numbers without decimals. Doing "Rearrange All Artboards" from the Artboards panel flyout menu was an automatic way to align the artboards to the pixel grid that also worked.
I believe this may have been the issue. I confirmed that this occurs with artboards that are not aligned to pixel grids. Ones that are aligned to pixel grid do not seem to have this issue.
I was going to state that a 100px by 100px artboard should result in an image with the same dimensions, but then pixel grid would be more confusing. My more recent files I noticed don't have this issue, simply because I had been using "Rearrange All Artboards" as part of my regular process.
Thanks for updating this thread!
Just as another addition, if you are working in measurements other than pixels (cm, in, pt, etc.), your odds of this artboard issue occuring increases.
I had a recent document where one of my artboards needed to have a decimal pt value. All the artboards that followed were then offset by that decimal value when doing "Rearrange all Artboards...".
Had to go back and manually move the affected artboards, so the top left XY values didn't start on a decimal pixel value.
For anyone wondering, this issue originated by iOS developer app icon image requirements where one image is defined as 83.5pt. Not a great measurement for Apple to use since @1x it will always have an anti-aliasing issue, even if they don't use that image size.
The problem is still caused by Illustrator poorly handling artboard coordinates, but I could see how few individuals would require this flexibility. Most people however discover this because of the problem it creates, not because they're looking for artboard manipulation.
This is the actual solution. Thanks.
Silly that half a pixel coordinate would make such an issue, but anyway... Tnx.
That's not helpful since I gave the solution to the problem above. There is a setting in Illustrator for artboard coordinates which can be set to any part of the pixel. Therefore your comment is completely unnecessary.
Set these numbers to whole numbers and the problem should go away.
Therefore your comment is completely unnecessary.
I was referring to your "silly" remark. Since half pixels don't exist and images can only contain whole pixels, your artwork has to be set up this way.
You are correct in your statement that "half a pixel coordinate" is possible, and "half a pixel" taken out of the context of your statement would potentially be invalid, but within the context of your statement is valid.
You are correct that "half pixels don't exist" in bitmap images and this does not conflict with the statement made by martinovski.
This is really an annoying bug that should be fixed. Exported images should not vary its size depending on artboard position!
On average I waste 30 minutes of my time per workweek trying to figure out a workaround in a thousand + dollar software (per year) fo these errors that honestly are not justifiable.
I'm away from my desk hence looking up this issue without checking whether it is indeed this same old problem of art boards bot say at full pixel locations. I'm guessing it is this as I see your answers are recent, but I presumed this issue must have been fixed by now as it's been years since it originated. I really wish they would actually fix stuff like this. The use case for these kind of outcomes must be so tiny I'm sure it would be easier for those people to work around it instead!.
I can confirm that this is still very much a bug as I was just bit by it on a large project for remarketing ads. Ended up just saving for web on each individual ad because I just found this post/workaround today. While not ideal, it will be added to the thought bank for web workflow each time I start a new document now.